The invention relates to a cutter plate which is particularly suitable for finishing cutters, in particular crankshaft finishing cutters.
It is necessary in the course of processing crankshafts to perform further processing steps, for example finish-milling steps, on a crankshaft blank or on a crankshaft which was pre-processed by means of rough milling. In the course of this processing it can become necessary, for example, to work the cylinder faces of cylindrical pins and simultaneously the flat surfaces adjoining the pin. For example, this relates to the crank pin, as well as the surfaces adjoining the crank pin, the so-called oil collars. A so-called relief groove is often provided between the flat surfaces and the cylinder face of the pin, which is also intended to be produced by means of a milling process.
As a rule, further processing steps follow the milling process, which can include, for example, grinding operations on the cylindrical pins and roller-burnishing processes on the relief groove. It is attempted here to perform the milling operation with such a quality that the subsequent processing operations can be reduced to a necessary minimum.
A disk milling cutter and a reversible plate suitable for this are provided by DE 197 39 366 A1, wherein the reversible plates are maintained in a radial direction against the tool body as so-called radial plates. The radial cutter plates are rectangular plates which have protrusions on two radially oppositely located corners, which are used for forming the relief groove at the crankshaft.
With this milling tool the same number of active cutters results for forming the relief grooves as for the other surfaces to be worked. However, an increased chip removal volume results in the area of the relief grooves, compared with the area of the cylinder face, for example. Moreover, the number of active cutter edges in the area of the circumferential surface is increased when it is intended to process particularly slim crank pins, so that succeeding reversing cutter plates overlap each other to a greater extent. As a result the lengths of the cutting arcs are then larger in the area of the relief groove than in the area of the crank pin, which can result in an increased outlay for finishing work at the relief groove.
The object on which the invention is based is derived from this, namely to create a cutter plate for a milling tool, as well as a suitable milling tool, which makes it possible to mill the oil collar, the relief groove and the crank pin of a crankshaft with the same tool in one operation, after which a finish-milling process, for example, finish-grinding, of only the crank pin should be required.
This object is attained by means of the cutter plate in accordance with claim 1, as well as the milling tool in accordance with claim 14.
The cutter plates are so-called tangential plates, i.e. they are designed for being mounted in plate seats the normal surface line of the bearing surface of which approximately points in the radial direction or the axial direction. In this case a surface of the plate seat is considered to be the bearing surface, against which the cutter plate is braced by means of a fastening device, for example a clamping screw. The tangential plate concept makes possible an increase in the number of teeth in the area of the relief grooves, even in connection with very slim crank pins, provided the cutter plates in accordance with the invention are employed. These have at least one protrusion on their cover surface for forming the relief groove, and at least one other protrusion on a lateral surface. It is possible in this way to assign a cutter plate seated on a bearing surface with an axial normal surface line to each cutter plate seated on a bearing surface with a radial normal surface line. This arrangement results in two cutting edges for the relief groove and one cutting edge for the cylinder face. The cutting edge for the cylinder face is constituted by a straight main cutting edge section. This arrangement results in particularly short cutting arc lengths in the relief groove. Remaining processing traces can be removed in a simple roller-burnishing process. If the processing accuracy following the finish-milling process is sufficient, the roller-burnishing process can be omitted.
Moreover, the result of roller-burnishing substantially depends on the quality of pre-processing. A very smooth surface (short lengths of the cutting arc) is already achieved prior to roller-burnishing by means of the finishing cutter of the invention and the cutter plate of the invention, so that again a very good roller-burnishing result can be achieved. Extensive tensions occur in the area of the relief groove during the subsequent operation of the crankshaft. Here the surface quality in the relief groove determines the tendency for the formation of cracks, and therefore the load-bearing ability of the crankshaft.
The first protrusion formed on the cutter plate can extend over the entire length of the cover surface of the cutter plate and can therefore extend from the lateral surface, which leads during use, to the lateral surface, which trails during use. In this case the protrusion is embodied as a rib oriented in the direction of movement. This constitutes a solution which can be easily produced and is rugged. However, if needed, this protrusion can also be interrupted in its center, so that it is for example divided into two protrusions arranged on the cover surface. The same applies correspondingly to the second protrusion arranged on a lateral surface of the cutter plate. In a view of the lateral surface which leads during its employment, or the lateral surface which trails during its employment which, for example, can be designed to be approximately trapezoidal, it can be seen that the protrusions are arranged on corners which are located diagonally across from each other, but on surfaces of the cutter plate which have a common edge, i.e. which adjoin each other. The installed positions of the cutter plates, wherein the first protrusion and wherein the second protrusion are active, differ correspondingly by a turn of approximately 90xc2x0. This corresponds to the different radial, or axial, orientation of the plate seats.
The protrusions have matching contours, i.e. matching cutting edges. This is in the sense that the main cutting edge of the first protrusion can be brought to overlap the main cutting edge of the second protrusion, once the cutter plates have been properly positioned. Because of this, both protrusions can be employed for forming the exact same relief groove and can remove chips of approximately the same thickness.
For example, the protrusions can be embodied as ribs which are arranged substantially parallel in respect to each other, thus in both installed positions each of the ribs points in the circumferential direction of the milling tool.
The cutter plate preferably has a cover surface which is divided into two surface areas, between which there is a recess. The surface areas can be narrow strip-shaped areas, for example, which are located on a common plane and each of which is adjoined by main cutting edges. The same as the lateral surfaces and the base surface of the cutter plate, these surface areas are preferably ground in order to obtain a precise work result at the crankshaft. While the other surfaces are embodied to be flat or convex, the cover surface has a concavely arched section. The latter is located at the base of the protrusion. The division of the cover surface into narrow, for example strip-shaped surface areas, between which the cover surface is located slightly lower, allows the grinding treatment of the cover surface with a grinding tool having only one grinding edge, in that the volume of material to be removed during the grinding process is minimized. The section between the two surface areas can remain rough. In this case the two ground cover surface areas constitute a precisely worked surface, which can be used as a bearing surface when the second protrusion is active (axially oriented plate seat in relation to the normal surface line of the bearing surface, also called xe2x80x9clateral plate seatingxe2x80x9d). The position of the main cutting edge is furthermore precisely fixed by the grinding process (radially oriented plate seat in relation to the normal surface line of the bearing surface, also called xe2x80x9ctangential plate seatingxe2x80x9d).